1. Field of the Invention
The present invention relates to a method for operating a fluid valve for controlling or regulating a fluid, having at least one movable valve component which is displaceable with the aid of at least one electrical actuating signal which contains at least one first actuating signal portion which causes an oscillating valve motion of the valve component.
2. Description of Related Art
Hydraulic systems are designed to be primarily current-controlled, using actuators for electrohydraulic actuations. In the current-controlled system, disturbance variables in the hydraulic system, such as fluctuations in a pressure supply system, for example, are typically adjusted via fixed hydraulic gates and tolerances. Adjusting the hydraulic system to various temperatures is therefore complicated, and it is not possible to adjust influences which change the system, such as contaminants, cuttings, and aging phenomena. The disadvantages of the current-controlled hydraulic system are counteracted by instead operating in a pressure-controlled manner. Adjustment of the disturbance variables is possible and easy to implement in pressure-controlled hydraulic systems. One disadvantage is that appropriate actuators which are required are frequently characterized by nonlinearity, volatility, and ambiguity.
In addition, regardless of whether they are current-controlled or pressure-controlled, actuators for electrohydraulic actuations of hydraulic systems have nonlinear behavior patterns, such as static friction to sliding friction transitions, which adversely affect control and disturbance behavior during a regulation. To counteract this, the actuators are provided with a low-frequency motion superimposition which in a current-controlled manner keeps movable parts of the actuators in constant motion. Static friction to sliding friction transitions are thus avoided. The motion superimposition is provided with a small motion amplitude to avoid creating interfering pressure changes. To be able to use such motion superimpositions in a targeted and efficient manner it is necessary to have accurate knowledge of friction parameters of the actuators, which requires that constant environmental conditions and actuators having low parametric scattering are present during manufacture of the actuators. Here as well, long-term influences such as aging phenomena are not taken into account during regulation of the motion superimposition.
A method of the above-mentioned type is disclosed in published international patent application document WO 2006037715. A solenoid valve is controlled with the aid of a pulse-width modulation signal to which an oscillating signal is added, which allows an armature of the solenoid valve to oscillate with constant small oscillations about a central position in a targeted manner.
U.S. Pat. No. 5,222,417 discloses an oscillating signal which sets a valve into oscillation, the oscillating signal being regulated on the basis of a flow rate.
Published European patent document EP 0929020 describes a method for controlling an electromagnetic proportional pressure control valve having an oscillation for the motion superimposition. The motion superimposition has no effect on the pressure which is regulated by the pressure control valve.
It is necessary to provide a method which in a simple manner allows a motion superimposition which is constant in spite of changing environmental conditions, parametric scattering of actuators, and long-term influences such as aging phenomena.